1. Field of the Invention
The present invention relates to aircraft fuel storage and delivery systems, in general and more particularly to a system and method for providing aerial vehicles with an extended external fuel stores configuration in order to increase effectively the fuel storage volume and fuel carriage capacity of the aerial vehicles.
2. Discussion of Related Art
The propulsion system of a typical aerial vehicle includes one or more power plants, such as engines, providing thrust and lift to the vehicle and associated fuel storage means, such as fuel tanks, to hold the fuel that feeds the power plants via appropriate fuel delivery means, such as fuel lines. The fuel storage means are distributed within and across the surface aerial vehicle in a volumetrically optimal manner. The manner of distribution differ among different types of aircraft but typical fuel stores consist of a plurality of potentially interconnected internal fuel containers, such as fuel tanks or fuel cells installed within the internal space of the fuselage or within the internal space of the wings. As the range, performance and efficiency of an aircraft depend among other factors on the quantity of fuel the aircraft is carried there is a constant research and development effort to optimize the quantity of fuel carried by an aircraft. The process is particularly significant in military combat aircraft due to the highly complex requirements expected from a combat aerial vehicle. A combat aircraft should have a substantially small size, power plants relatively large in relation to the body, advanced life support systems for the crew, advanced communications, command, control, safety, protection, high performance and a large variety of weapon stores. In order to increase the range, radius of action, and loiter time of a military aircraft as much as possible in addition to the internal fuel stores typically external fuel stores are carried. External fuel stores consist of aerodynamically structured fuel containers detachably carried on specific carriers, such as pylons, detachably installed on the lower wing area or the lower fuselage area of the aircraft. The carriage of external fuel stores further require the installation of an auxiliary fuel delivery and control system that enable the provision of fuel from the external stores to the engine in a controlled manner where the external system is integrated seamlessly with the internal fuel system. Thus, the external fuel system should include fuel tank carrier pylons for the carriage of the external fuel tanks, fuel delivery lines, power lines, and fuel delivery monitoring and control lines. In a typical military aircraft these elements are pre-designed and integrated into the aircraft systems during the design, development and manufacturing process.
The addition of external fuel stores substantially improves the range of the aircraft. Range is particularly critical to military aircraft. External fuel stores are force multipliers in the sense that an aircraft carrying external stores is capable of performing longer and therefore more efficient missions. The quantity of the fuel carried within the external stores is a function of the volume of the external fuel tanks and the number of the external fuel tanks installed. A wide variety of carriage capabilities provided according to the type of aircraft, mission objectives, and the like. A combat aircraft typically carries two or four external tanks under the wings and one or more external tanks on the underside of the fuselage. As a typical external tank holds about 260 to 600 gallons of fuel an optimally configured external fuel store is capable of significantly increasing the range of a combat aircraft.
External stores are typically attached to an aerial vehicle via specifically pre-determined locations distributed across the external surface of the aircraft typically referred to hard points, weapon stations, or external stores stations. Hard points capable of supporting functional fuel stores are typically referred to as “wet” points. “Wet” points provide not only appropriate suspension devices but also functional interfaces to the aircraft fuel system, such as specific fuel delivery line connections, electrical connectors utilized as monitoring and control interfaces and the like. A typical military aircraft includes a plurality of other hard points, weapon stations or external stores stations for the carriage of a variety of diverse aircraft stores, such as missiles, heavy ordnance, electronic counter measures, thrust augmentation units, and the like. These hard points are typically referred to as “dry” points. Some hard points (typically located on inboard stores stations) have dual functionality in such a manner that they are capable of supporting both “dry” stores such as heavy ordnance and “wet” stores such as external fuel tanks. Obviously “dry” points, which are typically located on outboard stores stations, are incapable of carrying functional external fuel stores due to the lack of fuel system delivery, fuel monitoring and fuel control interfaces required to be associated with the stations. The limitation concerning the carriage of external fuel stores on a limited number of hard points is a disadvantage to an aircraft as it substantially limits the range, the performance and the mission versatility of the aircraft.
For economical efficiency, organizational and operational reasons most military aerial vehicles are designed as multi-role platforms. Consequently modern military aircraft are provided with functional versatility, such as the capability of conducting a variety of missions including offensive counterair (OCA), defensive counterair (DCA), interception (AA), combat air patrol (CAP), close air support (CAS), suppression of enemy air defenses (SEAD), deep strike, anti-shipping (AS), anti-submarine warfare (ASW), electronic warfare (EW), reconnaissance, surveillance, or the combination of two or more of the above. Each specific mission profile requires weapon pairing or the assignment of optimal weaponry for the given mission. Weapon pairing involves the delivery of a particular load of a particular store or a specific mix of different store types and loads. The wide range of mission profiles required from modern military aerial vehicle necessitates the option of carrying a variety of stores and loads. As weapon pairing is a complex process an optimal stores carriage configuration for each required specific mission configuration is not always practical. As a result it is often the case that an aircraft performs a combat mission while carrying stores and loads below the maximum permissible carriage capacity, and even with non-utilized (empty) weapon stations. For example, for the performance of a long-range mission, such as imagery intelligence gathering, which requires a relatively limited load of weapons (for self-defense only) but needs substantially large quantities of fuel, the designated aircraft may take off with a non-optimal external stores configuration. The fuel load will be insufficient for the performance of the mission while some of the available “dry” weapon stations will not be usefully utilized. Similarly an aircraft prepared for an Air-to-Air mission (A/A) is typically required to carry air-to-air missiles only. In both of the above mentioned exemplary missions the stores carriage capacity of the vehicle is utilized in a non-optimal manner, as some of the available weapon stations are not usefully employed.
In order to enhance the range and the mission capabilities of an aerial vehicle the technique of aerial refueling was conceived, designed, and developed. Air refueling became a widely used technique wherein the fuel stores of an aircraft are periodically replenished in-flight from the stores of a specific tanker aircraft. Although this is a universally known, extensively refined and widely accepted procedure in the air forces of the world and under some circumstances its use is unavoidable, the technique has a number of disadvantages. Air refueling is a complex operation demanding very precise timetables, pre-defined rigid procedures, accurate maneuvering and very intensive planning. The operation is expensive in terms of the number of tanker aircraft required, which are typically high-priced large aerial vehicles flown and operated by a large extensively trained crew. The operation is highly problematic at night when lights should be used and practically impossible in adverse weather conditions. Additionally the insertion of tanker aircraft into a combat zone is a highly risky operation. Thus, tankers typically operate out of the limits of the combat zone. This fact necessitates that a receiving combat aircraft, which is low on fuel to break off the engagement or the mission, leave the combat area, spend a substantially extended period of time performing refueling and then return to the combat. When dealing with a complex air campaign involving hundreds of “shooters” and dozens of tankers it will be easily perceived that a high degree of inefficiency is involved in a campaign where the overall planning is based on aerial refueling as the force multiplier.
Another solution to the problem concerning the fuel quantity limitation of aircraft involves supplementing the external fuel stores by the addition of auxiliary fuel tanks to an aircraft. As the internal space of a typical aircraft is utilized to its full capacity the only option is the addition of external fuel tanks. As the number of “wet” points capable of carrying fuel stores is typically pre-defined and limited, in order to add auxiliary external fuel tanks the re-design and the modification of an existing “dry” point is required by the conversion of the original hard point to a dual functionality “wet/dry” point. Such a conversion is a long, expensive and complex process as it typically involves considerable changes in the internal structure of the aircraft, in the configuration of the internal fuel system, the associated control and monitoring systems, and the like. As was mentioned above the internal space of a modern military aircraft is already fully packed with a variety of critical equipment. Therefore installing additional equipment and re-arranging the configuration of existing equipment unavoidably involve complex procedures, high costs and high risks.
It will be easily perceived by one with ordinary skill in the art that there is an urgent need for a system and method to enhance the fuel carriage capacity of an aerial vehicle without the need to resort to extensive internal modifications in the structure of the aircraft and without extensively modifying the existing fuel systems of the aircraft. Preferably the system and method should be “transparent” to the aircraft and should be developed in manner as to be to be made substantially generic to a group of similar aerial vehicles.